1. Field of the Invention
The present invention relates to zirconia powder for colored zirconia sintered bodies which have no defects and have a jewel-like appearance showing deep black color and where temperature dependency of sintered body density, color migration, cracks, or the like are not observed. The present invention also relates to black zirconia sintered bodies which have no defects and have an excellent appearance, and pigments which are suited for black zirconia.
Priority is claimed on Japanese Patent Application No. 2006-139462, filed May 18, 2006, the content of which is incorporated herein by reference.
Black zirconia sintered bodies are widely used in ornamental articles (such as watch bands, exterior components for watches, watch cases, broaches, tie pins, cuff links, and fitting components of handbags), exterior components in various products (such as cell phones, home appliances, and mobile appliances), semiconductor components, structural components, or the like.
2. Description of the Related Art
Colored zirconia sintered bodies, especially black zirconia sintered bodies are conventionally known. For example, colored zirconia sintered bodies formed from zirconium oxides which contain a group of oxides of C, Cr, Co, Cu, Er, Fe, Ho, Mn, Nb, Ni, Pr, Tm, Ti, V, or the like and a stabilizer, have been proposed (e.g. Patent document 1). Although it is possible to use any colored elements when only blackening of zirconia sintered bodies is desired, various sintered bodies were achieved with different bending strength and/or color tones depending on the kinds of elements used and on their added amounts, which was a problem.
For example, a black zirconia sintered body has been reported where Mn is used as an essential coloring component (Patent document 2). However, the black color of the sintered body containing Mn was bluish- or reddish-black, or colors close to black, and the sintered body containing Mn with sufficient bending strength was also difficult to achieve.
In addition, black zirconia sintered bodies have been reported where pigments containing Cr are used (Patent documents 1 to 4). Although Cr-containing pigments are common as general black pigments, use of black pigments which do not use Cr is preferable as a measure in order to deal with environmental problems.
A black zirconia sintered body has been reported where CoFe2O4 spinel, which is a pigment that does not contain Cr, is added as a black pigment (Patent document 5). However, in the sintering of black zirconia where a pigment of Co—Fe type is used, coloring elements readily evaporate at high temperatures, causing a problem of contaminating the inside of facilities with the coloring elements (color migration). With such sintered bodies, color tones of the surface thereof deteriorate and it was necessary to grind the surface of the sintered bodies deeply. Moreover, due to the evaporating of coloring components, pores were readily generated on the surface of sintered bodies, which was a problem.
On the other hand, a method is known where Al2O3 is added in excess as an inhibitor for the evaporation of coloring components (Patent document 6). However, an excessive amount of Al2O3 is required with the conventional pigments, and since a sufficiently deep black color is not achieved, a reduced amount of Al2O3 has been used in order to achieve satisfactory color tones, although the occurrence of cracks or the like resulted in reduced production yield.    [Patent document 1] Japanese Unexamined Patent Application, First Publication No. Hei 10-81562 (page 4, section [0016])    [Patent document 2] Japanese Patent Publication No. 3010236 (page 2, column 4, line 3; page 4, section [0016])    [Patent document 3] Japanese Unexamined Patent Application, First Publication No. Sho 63-185857 (page 4, Table 1; page 5, Table 3)    [Patent document 4] Japanese Laid-Open Patent Application No. 2006-342036 (Claims 4 to 7)    [Patent document 5] Japanese Patent Publication No. 3714563 (Claim 1; page 3, section [0004])    [Patent document 6] Japanese Patent Publication No. 2535161 (page 2, column 4, line 20)
As described so far, although zirconia sintered bodies with black color tones are conventionally known to be achievable by the addition of various metal elements or by reduction sintering, black zirconia sintered bodies which satisfy the following features/conditions; i.e. high density, high strength, excellent color tones, and no defects; and a powder containing zirconia which satisfy the following features/conditions; i.e. high sintering yield at the time of producing black zirconia sintered bodies, no sintering-temperature dependency, and no color migration; have not been achieved.